In recent years, projection exposure apparatus for projecting and exposing a pattern of a mask onto a photosensitive substrate by using extreme ultraviolet light (EUV) in the wavelength region of about 5 to 40 nm as exposure light have been put into practical use. Reflection type optical systems are used (see, for example, Japanese Patent Application Laid-Open No. HEI 11-312638) in exposure apparatus for EUVL (extreme ultraviolet lithography), since glass materials exhibiting a high transmittance for short-wavelength light are limited.
In the projection exposure apparatus described in Japanese Patent Application Laid-Open No. HEI 11-312638, as shown in FIG. 6, laser light emitted from a non-EUV laser light source 201 and condensed by a condensing mirror 202 is caused to impinge at a point 204 onto a target material supplied by a nozzle 203, so that the target material is turned into plasma in response to intense energy, whereby EUV light is generated. Thus generated EUV light is condensed by a condensing mirror 205 and is reflected by a guiding optical system 206, so as to be made incident on an entrance-side fly-eye mirror 207 in which a number of concave mirrors are arranged in parallel. The light beam reflected by the entrance-side fly-eye mirror 207 passes through an aperture stop 208, so as to be reflected by an exit-side fly-eye mirror 209 in which a number of concave mirrors are arranged in parallel, and then passes through the aperture stop 208 again, so as to be made incident on an optical system 210. The light beam reflected by the optical system 210 is condensed by an optical system 211, so as to illuminate a mask 212. A pattern image of the illuminated mask 212 is projected and exposed to a wafer (photosensitive substrate) 214 through a projection optical system 213.